Organizing code in Visual Basic

last modified October 18, 2023

In this part of the Visual Basic tutorial we show how to organize code. We cover modules, procedures and namespaces, and the scope.

Visual Basic statements are organized into blocks, modules, classes and namespaces. This helps to make the code more maintainable and robust. Correct code organization prevents from making errors in the code.

The basic building blocks of a Visual Basic program are:

Assembly
Namespace
Modules
Classes
Procedures and functions
Blocks
Statements

An assembly is a DLL or exe file. An assembly is a compiled code library for use in deployment, versioning and security. A namespace is an abstract container providing context for the items. A module is a reference type available throughout its namespace. Classes are basic building blocks of an OOP program. A procedure is a unit of a program that is created to do a specific task. A block is the lowest level organisation of Visual Basic statements provided by some keywords like If or While. A statement is an atom in a Visual Basic program, a smallest unit of code.

Closely related to this topic is the scope and duration of a variable. A scope is the visibility of the declared variable.

Scope	Description
Block scope	Available only within the code block in which it is declared
Procedure scope	Available within the procedure in which it is declared
Module scope	Available to all code within the module, class, or structure in which it is declared
Namespace scope	Available to all code in the namespace in which it is declared

A lifetime of a variable is a period of time during which a variable holds a value. Local variables exists as long as the procedure is executing. After that, they are not available anymore. However, if we declare a variable to be Static, the variable continues to exist after the procedure terminates. Module, Shared and instance variables exist for the lifetime of the application.

The basic example

First, we cover some basics.

Program.vb

Option Strict On

Module Example

    Sub Main()

        Console.WriteLine("Simple example")

    End Sub

End Module

In this example, we have a Module called Example. Inside the example, we have a Main subroutine. The statement that prints some message to the console is placed within the Main procedure. Event the most simple Visual Basic programs must be properly organized.

Program.vb

Option Strict On


Public Class Example

    Public Shared Sub Main()

        Console.WriteLine("Simple example")

    End Sub

End Class

The exact example, now without the module. We can put the code inside a class too. The Main procedure must be declared Shared, because the class is not instantiated. The compiler calls the Main method without creating an instance of the class. That is why it must be declared Shared. Java and C# work the same.

Namespaces

Namespaces are used to organize code at the highest logical level. They classify and present programming elements that are exposed to other programs and applications. Within a namespace, we can declare another namespace, a class, an interface, a structure, an enumeration, or a delegate.

In the following code, we have two files that share the same namespace.

Program.vb

Option Strict On

NameSpace ZetCode

    Module Example1

        Public Dim x As Integer = 0

        Sub Init()

            x += 100
            Console.WriteLine(x)

        End Sub

    End Module

End NameSpace

We have a ZetCode namespace. In the namespace, we have a module Example1.

NameSpace ZetCode

We declare a namespace called ZetCode.

Public Dim x As Integer = 0

In the module, we declare and initialise a x variable.

Sub Init()
    x += 100
    Console.WriteLine(x)
End Sub

We have an Init method, in which we work with the x variable.

Program.vb

Option Strict On

NameSpace ZetCode

    Module Example

        Sub Main()

            Init()
            x += 100
            Console.WriteLine(x)

        End Sub

    End Module

End NameSpace

In the second file, we work with the Init method from the previous file.

NameSpace ZetCode

We work in the same namespace.

Init()
x += 100
Console.WriteLine(x)

We call the Init procedure and work with the x variable. Both the procedure and the x variable are defined in a different file and different module. But they are defined in the same namespace, so we can use them.

$ dotnet run
100
200

The following code example has two distinct namespaces. We use the Imports keyword to import elements from a different namespace.

Program.vb

Option Strict On

NameSpace MyMath

    Public Class Basic

        Public Shared PI As Double = 3.141592653589

        Public Shared Function GetPi() As Double

            Return Me.PI

        End Function

    End Class

End NameSpace

We have a skeleton of a Math class in a MyMath namespace. In the Basic class, we define a PI constant and a GetPi method.

Program.vb

Option Strict On

Imports MyMath

NameSpace ZetCode

    Public Class Example

        Public Shared Sub Main()

            Console.WriteLine(Basic.PI)
            Console.WriteLine(Basic.GetPi())

        End Sub

    End Class

End NameSpace

In this file, we use the elements from the MyMath namespace.

Imports MyMath

We import the elements from the MyMath namespace into our namespace.

Console.WriteLine(Basic.PI)
Console.WriteLine(Basic.GetPi())

Now we can use those elements. In our case the PI variable and the GetPi method.

Program.vb

Option Strict On

' Imports MyMath

NameSpace ZetCode

    Public Class Example

        Public Shared Sub Main()

            Console.WriteLine(MyMath.Basic.PI)
            Console.WriteLine(MyMath.Basic.GetPi())

        End Sub

    End Class

End NameSpace

Note that we do not need the Imports keyword. In the example, it is commented out. We can use elements from other namespaces by using fully qualified names of the elements.

Modules

A module is used to organize code and wrap up variables, properties, events, and procedures of similar use. Unlike a class, a module is not a type. A module can be created in a namespace or in a file. A module cannot be created inside another module, class, structure, interface or block. All members in a module are implicitly Shared. Modules have a Friend access. This means that a module is accessible everywhere in an assembly.

Program.vb

Option Strict On

Module First

    Public x As Byte = 11

    Public Sub FirstModule()

        Console.WriteLine("First module")

    End Sub

End Module

Module Second

    Public y As Byte = 22

    Public Sub SecondModule()

        Console.WriteLine("Second module")

    End Sub

End Module


Module Example

    Sub Main()

        Console.WriteLine(x)
        Console.WriteLine(Second.y)
        FirstModule()
        SecondModule()

    End Sub

End Module

We have three modules defined. The first two modules have variables and procedures. These will be used in the third module.

Module First

    Public x As Byte = 11
...
End Module

We can use access specifiers inside modules too. This way we can control the accessibility of the elements in the modules.

Console.WriteLine(x)
Console.WriteLine(Second.y)

We print the x and y variables. They are Public and are accessible from a different module. We may use the module name to fully specify the variable name.

A scope is a visibility of a variable. A variable with a module scope is available within the module, where it was declared.

Program.vb

Option Strict On

Module Example

    Private x As Integer = 0

    Sub Main()

        proc1()
        proc2()
        proc3()

    End Sub

    Sub proc1()

        Console.WriteLine(x)

    End Sub

    Sub proc2()

        x += 100
        Console.WriteLine(x)

    End Sub

    Sub proc3()

        x += 100
        Console.WriteLine(x)

    End Sub

End Module

We have x variable inside the module. The variable is available in all three procedures.

Private x As Integer = 0

This is a variable with a module scope. It is declared outside any procedure.

Sub proc2()
    x += 100
    Console.WriteLine(x)
End Sub

Inside the proc2 procedure, we increase the x variable and print its contents to the console. We refer to the x variable defined in the module.

$ dotnet run
0
100
200

Procedures

Procedures provide modularity to the code project. They should do only a specific task.

Program.vb

Option Strict On

Module Example

    Dim x As Integer = 0

    Sub Main()

        Console.WriteLine(x)

        proc1()
        proc2()
        proc3()

    End Sub

    Sub proc1()

        Dim x As Integer
        x += 100

        Console.WriteLine(x)

    End Sub

    Sub proc2()

        Dim x As Integer
        x += 100
        Console.WriteLine(x)

    End Sub

    Sub proc3()

        Dim x As Integer
        x += 100
        Console.WriteLine(x)

    End Sub

End Module

In the preceding code example, we have three procedures beside the main procedure. The three procedures create a local x variable and print it to the terminal. The main procedure refers to the module x variable.

Sub proc1()
    Dim x As Integer
    x += 100
    Console.WriteLine(x)
End Sub

The proc1 procedure creates a local x variable. This variable shadows the one, declared at a module scope.

$ dotnet run
0
100
100
100

The main procedure prints 0. The other procedures print 100 to the terminal. They create their local x variables, initiate them to 0, increase by 100.

Block scope

It is important to understand that variables declared within a block of code like If/End If or While/End While have a limited block scope and lifetime. The next example illustrates this.

Program.vb

Option Strict On

Module Example

    Sub Main()

        If True

            Console.WriteLine("Inside If block")

            Dim x As Integer = 0
            Console.WriteLine(x)

            x += 500
            Console.WriteLine(x)

        End If

        Console.WriteLine("Outside If block")

        Rem Will not compile
        Rem Console.WriteLine(x)

    End Sub


End Module

We have an x variable declared Inside the If/End If block.

Rem Will not compile
Rem Console.WriteLine(x)

The variable is not available outside the block. If we uncomment the second line, the example will not compile.

This part of the Visual Basic tutorial was dedicated to organizing code.

Ebooks

Organizing code in Visual Basic

The basic example

Namespaces

Modules

Procedures

Block scope